Wireframe node has no effect on bumpmap
There appears to be an issue with that node in conjunction with the Bump node. One solution that appears to work is using the Wireframe node in conjunction with a Normal Map node:



These nodes render a result like this:



Notice that these values can be inverted as well:



One word of warning thanks to @WChagrin:


  I would say that that's almost certainly undefined behavior. The colored pixels in the normal map are supposed to represent unit vectors in tangent space. When the wireframe node outputs a value of 0, that's coerced into the vector &lt;0, 0, 0>, which is not only non-unit, but non-normalizable. That is, trying to normalize it would require division by zero. Relying on this behavior is probably a Bad Idea™.